The present invention relates to a gradient index rod lens, a method for manufacturing a gradient index rod lens, and a lens array.
A gradient index rod lens is manufactured by performing a treatment, such as ion exchange, on a cylindrical piece of glass. This distributes refractive indexes from the central portion of the lens to the peripheral portion of the lens. The refractive indexes at the peripheral portion of the lens normally are not included in the intended gradient index rod range. Thus, the peripheral portion of the lens cannot be used. For example, referring to FIG. 27, a gradient index rod lens 11 has an effective portion 12. The effective portion 12 is located in the center of the gradient index rod lens 11 and has a diameter, which is denoted by De. Aberrations are tolerated In the effective portion 12. A peripheral portion 13 is defined around the effective portion 12. The refractive indexes distributed in the peripheral portion 13 are not included in the intended range. Accordingly, the diameter Do of the gradient index rod lens 11 is determined by adding a value obtained by multiplying the width of the peripheral portion by two to the effective diameter De of the effective portion 12. Since the refractive indexes distributed in the peripheral portion 13 are not included in the tolerable range, the focal point of the light that passes through the peripheral portion 13 differs from that of the light that passes through the effective portion 12. This produces a large aberration in the lens as shown by FIG. 28.
The conventional gradient index rod lens has a diameter that is significantly greater than the effective diameter of the effective portion 12, which is the portion actually functioning as a lens. Thus, when a plurality of gradient index rod lens are arranged to form a lens array 21, as shown in FIG. 29, the lenses increases the size of the lens array 21 and the pitch between effective portions 12. This lowers resolution. In the example shown in FIG. 29, the gradient index rod lenses 11 are arranged in V-shaped grooves of a substrate 22. To reduce the size of the lens array 21, the diameter Do of the lens may be decreased. However, this would decrease the area of the effective portion and decrease the amount of the light that enters the effective portion 12.
A planar micro-lens array has been proposed to decrease the size of a lens array. In one type of lens array, the gradient index rod is such that the refractive index differs at different depths in a substrate. In another type of lens array, the surface of a lens array is etched to form pits, and resins hating different refractive indexes are filled in the pits. However, satisfactory lens characteristics cannot be obtained when such lens arrays are used to connect optical fibers with optical devices.
It is an object of the present invention to provide a smaller gradient index rod lens without decreasing the amount of light that enters its effective portion.
To achieve the above object, the present invention provides a gradient index rod lens including a lens body radially distributing refractive indexes. The lens body has a cross sectional outline formed by removing at least part of a peripheral portion of a cylindrical original lens body.
A further perspective of the present invention is a method for manufacturing a gradient index rod lens. The method includes preparing a cylindrical original lens body and forming a lens body having a predetermined cross sectional outline by removing at least part of a peripheral portion of the original lens body.
A further perspective of the present invention is a lens array including at least a row of a plurality of gradient index rod lenses. Each of the gradient index rod lenses includes a lens body radially distributing refractive indexes. The lens body has a cross sectional outline formed by removing at least part of a peripheral portion of a cylindrical original lens body.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.